Frequency base knife control systems

ABSTRACT

Digital systems for controlling continuously rotating, variablespeed cutoff knives to provide precise control of the lengths of sheets cut from high-speed moving corrugated boards or webs. A main motor acts through a clutch to drive a double-facer that forms and advances a continuous strip of corrugated board. A slitter slits the board at the middle to form two strips. A top knife cuts one of the strips into sheets and a bottom knife cuts the other strip into sheets. The main motor drives a mechanical variable speed (Reeves) drive and a cyclic mechanism for each knife. Each knife is provided with a frequency based control system that acts through an associated correction motor to adjust its Reeves drive closely to control the cutoff length to a selected value. For this purpose, a web rider generates a reference pulse for each one-sixteenth inch of board. A tachometer generator provides 1,600 feedback pulses each revolution of the knife, a portion of which may be preselected at thumb wheel switches to select the desired length of sheets. The frequency based control system responds to the frequency and phase of preselected feedback pulses and the reference pulses to provide a knife speed correction signal and a position or phase correction signal for precise control of the correction motor at any time that there is error. The system is preset by first switching from the web rider pulse generator to a preset pulse generator operated from the main motor to adjust the system close to the desired cutoff length before any board is run to prevent waste. A second set of thumb switches affords presetting of the sheet length for the next order while the system is running preparatory to switchover. A presettable sheet counter automatically displays the number of sheets remaining to be cut and stops the system when the selected number of sheets has been cut or may be used to start operation of an automatic order changer. An add-on counter allows selection of an additional number of sheets to be cut while the system is operating. A sheet length readout displays the actual cut length of alternate sheets within a hundredth of an inch. A footage counter displays the total length of board used on an order in 10 foot increments.

United States Patent [72] lnventors Arthur F. Allison Rlehfield; Siegfried R. Salzbrenner, Milwaukee, both of, Wis. [21 Appl. No. 835,945 [22] Filed June 24, 1969 [45] Patented Sept. 14, 1971 [73] Assignee Cutler-Hammer, Inc.

Milwaukee, Wis.

[54] FREQUENCY BASE KNIFE CONTROL SYSTEMS 19 Claims, 5 Drawing Fig.

[52] U.S. Cl 83/76, 83/522 511 Int. Cl 826d 5/24 [50] Field of Search 83/76, 522; 235/1 15.1

[56] References Cited UNITED STATES PATENTS 3.175.442 3/ 1965 Drenning 83/76 3,244.863 5/1966 Paterson 83/76 X 3,267,781 8/1966 Stems et al. 83/76 X 3.2764547 10/1966 Lewis, Jr. et a1. 83/76 UX 3,355,973 12/1967 Rubinstein et al. 83/76 3,411,388 11/1968 Rappaport 83/76 Primary Examiner-James M. Meister Attorney-Hugh R. Rather VI NAB sow BUY! trol of the lengths of sheets cut from high-speed moving corrugated boards or webs. A main motor acts through a clutch to drive a double-facer that forms and advances a continuous strip of corrugated board. A slitter slits the board at the middle to form two strips. A top knife cuts one of the strips into sheets and a bottom knife cuts the other strip into sheets. The main motor drives a mechanical variable speed (Reeves) drive and a cyclic mechanism for each knife. Each knife is provided with a frequency based control system that acts through an associated correction motor to adjust its Reeves drive closely to control the cutoff length to a selected value. For this purpose, a web rider generates a reference pulse for each one-sixteenth inch of board. A tachometer generator provides 1,600 feedback pulses each revolution of the knife, a portion of which may be preselected at thumb wheel switches to select the desired length of sheets. The frequency based control system responds to the frequency and phase of preselected feedback pulses and the reference pulses to provide a knife speed correction signal and a position or phase correction signal for precise control of the correction motor at any time that there is error. The system is preset by first switching from the web rider pulse generator to a preset pulse generator operated from the main motor to adjust the system close to the desired cutoff length before any board is run to prevent waste. A second set of thumb switches affords presetting of the sheet length for the next order while the system is running preparatory to switchover. A presettable sheet counter automatically displays the number of sheets remaining to be cut and stops the system when the selected number of sheets has been cut or may be used to start operation of an automatic order changer. An add-on counter allows selection of an additional number of sheets to be out while the system is operating. A sheet length readout displays the actual cut length of alternate sheets within a hundredth of an inch. A footage counter displays the total length of board used on an order in 10 foot increments.

FREQUENCY BASE KNIFE CONTROL SYSTEMS BACKGROUND OF THE INVENTION Frequency based knife control systems have been known heretofore.

Sanford M. Strand copending application Ser. No. 737,409, filed June 17, 1968, now Pat. No. 3,521,529, dated July 21, 1970, and assigned to the assignee of this invention, discloses a knife control system having a frequency based regulator for controlling the speed of the knife-driving motor. In such system, the strip of material is driven by one motor and the knife is driven by a separate motor. The speed of the knife motor is continuously controlled with respect to the speed of the material strip to cut off preselected lengths of sheets. A constant frequency bias maintains the correction signal at sufficient strength to insure speed correction even at slot speed.

The present invention relates to improvements thereover.

SUMMARY OF THE INVENTION Advantages can be realized in knife control systems by driving the knife or knives from the same main drive that drives the web. This is most conveniently done through a mechanical variable speed drive such as a Reeves drive individual to each cutoff knife.

The present invention relates to systems of that type and to use of a frequency based regulator for controlling a correction motor that adjusts the variable speed knife drive mechanism. In this way, continuous control is not required since the correction signal need operate a relatively small correction motor to adjust a Reeves drive only when an error is being corrected and the motor then stops.

An object of the invention is to provide an improved frequency based knife control system.

A more specific object of the invention is to provide an improved digital control system for cutoff knives that provides greater flexibility in operation than other known systems including presetting of the knife speed before web is run.

Another specific object of the invention is to provide a frequency based control system for adjusting a motor driven mechanical variable speed drive to a preselected control value.

Other objects and advantages of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1a through when assembled as shown in FIG. 2 show a partly schematic diagram of a frequency based knife control system constructed in accordance with the invention; and

FIG. 3 shows details of the position pulse generator of FIG. 1b.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. la, there is shown a high-speed cutoff machine for cutting sheets from a moving web. This web is shown as a corrugated board 2. A double-facer 4 or the like forms this corrugated board by applying a pair of elongated backing sheets to a corrugated core. This board leaves the double-facer at a high speed and passes over a stationary plate 6 to a slitter 8. This slitter slits the board at or near the middle to form two strips 2:: and 2b. Strip 2a is fed past a top knife 10 that is controlled to cut the strip into sheets of desired length. In a similar manner, strip 2b is fed past a bottom knife 12 that may be controlled to cut this strip into sheets of desired length.

The apparatus for controlling the top knife is shown. The portion of this apparatus that must be duplicated for controlling the bottom knife has been omitted to avoid undue complication of the drawing. The multiples marked B show connections to bottom knife control apparatus.

As shown in FIG. 1a, a main drive motor M powers a number of devices as indicated by the broken lines. This motor drives double-facer 4 through a clutch CL. This motor drives a mechanical variable speed drive 14 such as a Reeves drive for the top knife. As shown by the multiple B leading from the broken line illustration of the main drive shaft, the main motor may also drive a similar Reeves drive for the bottom knife.

A cyclic mechanism 16 cycles the knife speed on each knife revolution. For example, this cyclic mechanism may cause a sudden increase in the knife speed at the point of cutting so that a clean cut is made followed by deceleration to the former speed after the web has been sheared and the knife is clear thereof. A similar cyclic mechanism would be provided for the bottom knife.

A web rider 18 is mounted between the double-facer and the slitter with its wheel 18a engaging corrugated board 2 over plate 6. This plate below the moving web supports the latter to insure good tracking by the web rider wheel through gravity or slight spring load so that there is no significant slippage between the wheel and the moving web.

As this web rider wheel is rotated by the moving web, it operates a pair of pulse tachometers PTl and PT2 and a reed switch RS shown schematically in FIG. la. As the name implies, these pulse tachometers generate electrical pulses in response to movement of the web. Pulse tachometer PTl is a cutting reference tachometer generator that provides one pulse per l/ l 6 inch of moving board. Pulse tachometer PT2 is a display tachometer generator that provides one pulse per 1/100 inch of moving board. Reed switch RS provides one pulse per 10 feet of moving board to measure the length used.

As will be apparent from the drawing, these reference pulses of tachometer PTl control the length of sheets cut from the strip in connection with feedback pulses hereinafter described. These display pulses of tachometer PT2 control a sheet length readout device 20 shown in FIG. 1b that displays the actual length of the cut sheets. These reed switch pulses control a footage counter 22 that shows how many feet of web has been used.

In order to avoid wasting material by cutting incorrect length sheets, the system is preset very close to the desired setting before any web is run. For this purpose, a preset reference tachometer generator PT3 is provided. As shown in FIG. 1a, this tachometer is driven by the main motor. It provides one pulse per 1 16 inch of simulated board since it is not actually driven by the board. The frequency based regulator is first switched to tachometer PT3 to adjust the variable speed drive to the preselected sheet length as determined by the speed of the main drive and is then switched to tachometer PTl as soon as the web is started running by engaging the clutch CL to adjust the variable speed drive to the preselected sheet length as determined by actual measurement of the board.

In order to relate the knife motion to the web motion, there is provided a top knife feedback tachometer generator PT4. This tachometer is shown in FIG. la as being driven by the mechanical coupling between the variable speed drive and the cyclic mechanism and provides 1,600 pulses per knife revolution. The bottom knife would be provided with a similar feedback driven by the apparatus individual thereto whereby the two knives could cut the same length or different lengths of sheets in accordance with their settings.

As aforesaid, reference pulses are produced at the rate of one pulse per l/l6 inch of board and feedback pulses are produced at the rate of 1,600 per knife revolution. This means that without deletion of any feedback pulses, the knife would cut a inch sheet at each revolution thereof. Actually the system is arranged to afford selection of the sheet cutoff length from 20 inches or less up to 199 15/16 inches in 1/16 inch increments.

With maximum web speed of 600 FPM and maximum knife speed of three cuts per second, the sheet length would be 40 inches. With the web speed reduced to 300 FPM, as short as 20 inch long sheets could be cut.

The remainder of apparatus shown in the drawings will be described in connection with the following description of operation thereof Various component circuits including logic circuits and solid-state circuits. that are well known will be described only generally and specifically identified at the end of the specification as to type and manufacturer.

FREQL'ENC Y BASED REGULATOR OPERATION To provide a general idea how the frequency based regulator functions to provide adjustment of the sheet length at any time that error occurs, reference may first be had to FIGS. la and lb.

As aforesaid, cutting reference tachometer PT 1 located in the web rider converts board motion into a pulse train. One pulse is generated for each 1/16 inch of board. This pulse train is used as a reference frequency for both the top and bottom knives. These pulses are shaped to near square wave 10 volt pulses in a NOT logic N l for the top knife.

At the same time, feedback tachometer PT4, driven by the output shaft of the mechanical variable speed drive, converts knife rotation into a pulse train. A total of 1,600 pulses are generated for each knife revolution.

This feedback pulse train is shaped to near square wave pulses of 10 volts in a NOT logic N2 and fed into a counter. This 2 counter consists of three cascaded four-bit counter units, the first two of which, BCDl and BCDZ, are binary coded decimal counter units and the third, BCI, is a binary counter unit.

These counter units divide the input frequency into the following percentages, and considering an input of 1,600 pulses, are representative of the following proportions of pulses and sheet lengths in inches at the various counter outputs:

The manner in which a binary counter provides output pulses in response to input pulses is shown below:

Input pulses..... l '2 3 4 5 6 7 8 9 10 ll 12 13 14 15 16 Output pulse T-..... 1 0 l 0 1 0 1 0 1 t) 1 (l 1 0 1 0 A binary coded decimal counter operates like the above binary counter for nine input pulses but all outputs go to 0 (reset) on the tenth input pulse.

It will be apparent from the foregoing that for 10 input pulses, output T of counter unit BCDl goes positive (1 five times for a 50 percent output. Output P goes positive twice for a 20 percent output. And outputs K and C each go positive once for 10 percent outputs.

Since counter unit BCDZ is cascaded to counter unit BCDl, its outputs provide the percentages shown in the above table.

Counter unit BCI is a straight binary counter. From the foregoing, it will be seen that its output T goes positive eight times for 16 input pulses for a 50 percent output. lts output P goes positive four times for a 25 percent output. Its output K goes positive twice for a 12.5 percent output. And its output C goes positive once for a 6.25 percent output. Due to cascading, these percentages are reduced to the amounts shown in the above table.

Thus, it will be seen that the counter units produce outputs corresponding to linear inches in tens, units and fractions, respectively, up to 99 15/16 inches as shown in the third column above. This means that a sheet up to 99 15/16 inches long may be cut if no feedback pulses are deleted, and shorter sheets in 1/16 inch decrements may be cut by deleting pulses.

In order to cut sheets up to 199 15/16 inches long, for each revolution of the knife, 1,600 pulses are added in parallel with the cascaded counter units. That is, the input frequency is also applied from NOT logic NZ to NOT logic N3 wherein a complement of the input frequency is produced to avoid coincidence between pulse edges.

Sheet length control thumb wheel switches SLCl are set to select certain portions of these pulses per knife revolution, thus establishing a corresponding sheet length by deleting the remaining pulses.

The selected portions of these pulses are applied to the inputs of a scaler circuit SCI. This scaler circuit receives the several frequencies at its inputs and combines them into a single frequency; that is, it converts several channels of synchronized, variable width pulses with noncoincident leading edges into a single channel of constant width output pulses, with one output pulse for each input pulse. The output of the scaler circuit is the actual feedback frequency that is used for control purposes.

A second sheet length control switch SLC2 and a second scaler circuit 8C2 are provided to allow selection of the sheet length for the next order while the present order is being filled. A transfer relay TTR is used to select the proper scaler circuit and sheet length control switch associated therewith.

Referring to FIGS. 1a and 1b, the reference frequency coming from NOT logic N1 is converted in one channel F-K of an output pulse generator circuit OPG into a pulse train of constant pulse width, with the frequency depending on the speedof the corrugated board, called speed reference. At the same time, the feedback frequency coming from the scaler circuit is converted in another like channel 13-5 of the output pulse generator into a pulse train of constant pulse width, with frequency depending on the knife speed, called speed feedback. These two pulse trains, amplified to 24 volts amplitude in power AND logics Al and A2, respectively, are used for speed regulation in the correction motor control system as hereinafter more fully described.

In addition to such speed regulation, position regulation in terms of phase displacement between reference and feedback pulses is provided. The phase displacement between reference and feedback pulses is directly proportional to the error dis placement between a given rotary position of the knife blade I and a properly corresponding point on the corrugated board at any instant of time.

For this purpose, the reference and feedback frequencies are also fed into four-bit binary counter units BCZ and 3C3, respectively, that may divide these frequencies by 2, 4, 8 or 16, depending on the output T, P, K or C, respectively, that is used, 8 in the illustrated system. These counter units may be used to provide one pulse for every 91;, /4, is or 1 inch of corrugated board, r in the illustrated system. These binary counters afford selection of the gain for the best performance of the position regulator. In other words, they avoid making it too sensitive and prevent hunting.

Pulse canceller circuit PC provides an anticoincidence function and puise shaping function needed to drive a position pulse generator circuit PPG. A positive pulse introduced into input D of the pulse canceller circuit will normally produce a long microsecond negative pulse at output K followed immediately by a short 5 microsecond negative pulse at output P.

In a similar manner, a positive pulse introduced into input S will normally produce a long 120 microsecond negative pulse at output T followed immediately by a short 5 microsecond negative pulse at output P. If the leading edges of the pulses introduced into the inputs D and S are within 200 microseconds of each other, no outputs will occur. In other words, substantially coincident pulses will be cancelled.

This pulse cancellation means that no position correction will take place if the reference and feedback pulses have a phase displacement within a predetermined limit, in this case, 200 microseconds, because the pulse canceller will provide no output pulses. On the other hand, if the phase of the reference pulses leads the feedback pulses by more than 200 microseconds, the pulses will be noncoincident and output T will provide a larger number of pulses than output K of the canceller. These will cause the knife position to be advanced as hereinafter described. Conversely, if the phase of the feedback pulses leads the reference pulses by more than 200 microseconds, the pulses will be noncoincident and output K of the canceller will provide more pulses than output T. This will retard the knife position as hereinafter described.

The outputs of the pulse canceller are applied to a position pulse generator PPG.

Position pulse generator PPG in FIG. lb is initially set or reset into its center, no output condition, that is, a bit is preset into its output 3 that has been left disconnected. From this midposition the bit shifts up in response to pulses at its input L and shifts down in response to pulses at its input F, and consequently oscillates between adjacent outputs in response to pulses at both inputs L and F depending upon the relative frequencies of these input pulses. If the frequencies of these input pulses differ, their phases correspondingly differ or if the frequencies are equal and their phase differs this indicates the position error between the corrugated board and the cutoff knife.

For example, if the pulses at input L have a leading phase relative to the pulses at input F, the bit will oscillate between outputs 3 and 4. A first pulse at input L will shift the bit from output 3 to output 4. A pulse coming thereafter to input F will shift the bit back to output 3. If two pulses arrive at input L in direct sequence, the bit will shift from output 3 to output 4 and to output 5. The bit could then oscillate between outputs 4 and 5 if input L is two pulses ahead ofinput F.

In a similar manner, the bit will shift between outputs 3 and 2 or between outputs 2 and 1 when the pulses at input F lead those at input L by one or two pulses.

It will be apparent from FIGS. and lb that upward shifting of the bit to outputs 4 and 5 of position pulse generator PPG is indicative of the sheets being out too short. This is due to the knife position leading the board position resulting in pulses into input L with these pulses to have a leading phase relative to the pulses at input F, These bits at outputs 4 and/or 5 will produce a position slower" signal as hereinafter described,

Conversely, downward shifting of the bit to outputs 2 and l is indicative of the sheets being cut too long. This is due to the fact that the knife position lags the board position resulting in pulses into input F with these pulses to have a leading phase relative to the pulses at input L. The frequency of the pulses at input F corresponds to the speed of the corrugated board and is intended to remain unchanged once the speed of the main drive motor has been set at a predetermined value.

The system is arranged so that whenever it is stopped and restarted, a bit is put into the center output 3 of position pulse generator PPG. This is done by normally open contact 1 and normally closed contact 2 of reset relay RES whereby input R is disconnected from, and input K is connected to, output P of the pulse canceller whenever the system is not running. During such time, with power being connected, plus 10 volts is applied from the pulse canceller into input K of the position pulse generator. This plus 10 volts is applied, as shown in FIG. 3, through resistor R18 to the base of transistor O5 to render this transistor nonconducting. Consequently, current will flow from positive voltage at supply terminal A through the emitter-base circuit of transistor Q6 and resistor R16 to zero voltage at supply terminal V to render transistor Q6 conducting thereby putting an initial bit 1 into output 3. This bit is plus 10 volts at output 3.

At the same time, any bits that there might have been at outputs I, 2, 4 and 5 are removed. This is done by clearing the first, second, fourth and fifth flip-flops to their 0 conditions. For this purpose, current flows from positive voltage at supply terminal A through the emitter-base circuits of transistors 01, Q3, Q7 and Q9 and respectively associated resistors R3, R10, R24 and R31 in parallel and then through common resistor R34 to zero volts at supply terminal V to render these transistors conducting. This puts outputs l, 2, 4 and 5 at zero volts that constitutes removal of a bit at any of them.

Referring to FIG. 3, it will be seen how the bit is shifted from output 3. Such shifting will take place whenever a long I20 microsecond) negative pulse comes into input L or F followed immediately by a short (5 microsecond) negative pulse to input R of position pulse generator PPG. It is assumed that reset relay RES has been energized as hereinafter described to close its contact 1 and open its contact 2.

To described the shift, a long negative pulse (plus 10 volts to zero) on input F causes capacitor C3 to charge. The circuit is from positive supply terminal A through the emitter and collector of transistor Q6, resistor R13 and capacitor C3 to zero volts at input F. The duration of this pulse allows capacitor C3 to charge. At the end of this pulse when input F goes back to plus 10 volts, capacitor C3 raises the voltage at the base of transistor Q3 above plus 10 volts, because the capacitor cannot discharge immediately, to turn transistor Q3 off. As a result, transistor Q4 turns on by current flow from positive supply terminal A through its emitter and base and resistor R9 to terminal V. Consequently, output 2 goes to plus 10 volts that means that the bit has been shifted thereto.

The bit at output 3 is removed by the short pulse on input R that follows the long pulse on input F. The leading edge of the short pulse may coincide in time with the trailing edge of the long pulse. This short negative pulse as shown at the lower left portion of FIG. 3 causes current flow from positive supply terminal A through the emitter-base circuits of transistors Q1, Q5, Q7 and Q9 and resistors R3, R17, R24 and R31, respec tively, to cause these transistors to conduct. This clears away the bit from output 3. The discharge time of capacitor C3 is longer than this short clear" pulse so that transistor 03 remains off and transistor Q4 remains on. This completes shifting the bit from output 3 to output 2.

If the next pulse comes in at input F, the bit will shift in a similar manner to output 1. However, if the next pulse instead comes in at input L, the bit will shift back to output 3. The next pulse at input L will shift it to output 4, etc. Actually, since pulses come to both inputs F and L, the bit will shift back and forth between a pair of outputs.

If a number of pulses come into input F, the bit will shift to output 1 and remain there. It will not shift out of the circuit in response to another pulse at input F. This is prevented by diode D1. When transistor Q2 is conducting, a bit at output 1, and a pulse comes into input F, this diode allows capacitor C l to charge. This charge prevents the short clear pulse from resetting the first flip-flop to 0 so that the 1 bit remains at output I.

In a similar manner, diode D10 prevents the 1 bit from shifting offfrom output 5 in response to another pulse at input L.

Bits at outputs 2 and 1 of position pulse generator PPG in FIG. lb are applied to inputs M and L, respectively, of output pulse generator OPG. In a similar manner, bits at outputs 4 and 5 are applied to inputs S and R, respectively. These oscillating bits received from outputs 2 and l or both are converted in an OR logic power amplifier in output pulse generator OPG into a pulse train. In a similar manner, the oscillating bits received at other times from outputs 4 or 5 or both are converted in another like OR logic power amplifier in the output pulse generator into a pulse train. These pulse trains appear at outputs P and T. respectively. These pulse trains have a pulse width depending upon (proportional to) the amount of dis placement and a frequency depending upon (proportional to) the speed of the corrugated board. By amount of displacement tact is closed. The tens switch unit T will pass from 10 to 90 output pulses for 100 input pulses depending on what position it is set. Units switch unit U will pass from one to nine output pulses for K) input pulses in accordance with its setting. And

is meant the error displacement between a given fixed point fractions switch unit F will pass from one to 15 output pulses on the corrugated board and a properly corresponding rotary for 16 input pulses depending on its setting. position of the knife blade. With the above in mind, sheets 154 /4 inches long will These two pulse trains are used for position regulation in the require setting hundreds unit H to its position 1, setting tens correction motor control system as hereinafter described. unit T to position 5, setting unit U to position 4, and setting To summarize the foregoing description of the frequency fractions unitF to position 4 since four-sixteenths is V4. based regulator, for speed correction, whenever the reference To select a quantity of 67 sheets, count select units switch pulse frequency is greater than the feedback pulse frequency US and tens switch TS are set at 67 as shown in FIG. 1c. as when the knife speed is too low, power AND logic Al pro- Assuming that electrical power has been connected to the vides a higher frequency of constant width pulses than power system, it is now ready for operation. AND logic A2. On the other hand, whenever the feedback This connection of power causes a bit to be set into output 3 pulse frequency is greater than the reference pulse frequency of position pulse generator PPG and any bits at outputs 1, 2, 4 as when the knife speed is too high, power AND logic A2 proor 5 thereof to be cleared away as hereinbefore described. vides a higher frequency of constant width pulses than power Main motor M may then be started running to drive preset AND logic Al. These two pulse trains will immediately be reference tachometer ITTB and mechanical variable speed recognized as convenient inputs to an integrator to run a cor- 2o drive 14. Cyclic mechanism 16 and feedback tachometer PT4 rection motor in a forward or reverse direction as hereinafter are driven by variable speed drive 14 in accordance with its described. speed setting. Cyclic mechanism 16 drives top knife 10 and Also, for position correction, whenever the reference pulses reset reed switch RRS. The function of this reset reed switch is have a leading phase displacement more than a predetermined to start and stop the sheet length readout device on successive amount as aforesaid, output P of the output pulse generator revolutions of the knife. provides a pulse train having a pulse width proportional to To preset the system for the correct length of cut as close as such displacement. Altematively. whenever the feedback pulpossible before web is run and to transfer the setting of count ses have a leading phase displacement more than such select switches US and TS to sheet counters UC and TC, it is amount, output T of the output pulse generator provides a necessary to press the preset switch in FIG. lc. Alternatively, pulse train having a pulse width proportional to such displacesuch count transfer can be done by pressing the count transfer ment. These pulse trains, whichever one occurs, will be recogswitch in FIG. 1c that is in parallel with contact 1 of the preset nized as a convenient input to an integrator to rotate a corpushbutton switch. rection motor sufficiently to bring the reference and feedback A a r l of this preset switch operation to close its conpulse phases into coincidence within the predetermined limit ac 1, top knife count transfer relay CTR is energized acro of 200 microseconds. the 24 volt DC supply P-N. This relay closes its contacts 1 and 3 and opens contact 2. Contact 1 connects positive voltage SYSTEM QPERATION from supply line P therethrough and through units count select switch US at setting 6 to contact 7 of units counter UC. Having no described how the frequency Pased rfigulafor This positive voltage is also applied through tens count select functions, h Operation of the System conluncnon switch T8 at setting 7 to contact 8 of tens counter TC. This there i h will be describfid' marks the units and tens counters for a predetermined setting.

Let it be assumed that it is desired to cut sheets 154% inches While only two count select switches and two counters, long for a total quantity of 67 sheets. units and tens, have been shown, it will be apparent that addi- For this purpose the four units of selected length control tional count select switches and sheet counters may be conswitch SLCl in FIG. la are set to the proper positions. This acted m a slmllr manner as mdlcated y arfows HS and HC switch may be of the thumb wheel type. Hundreds unit H, tens and the broken m the PF X The arrow unit T and units switch unit U may each have 10 operating g 21: a hundreds dlglt switch! thousandths i i positions marked 100 to 900 and 0, 10 to 90 and 0, and i m 9 i t: e 32%,"? my hundredths 2" and 0 whereas fractions unit F may have 16 operating posicounter. l 5 counter ions marked 1 to 15 and In the 10 operating positions of Continuing with counter transfer relay CTR operation, its each decimal switch unit, the four contacts close in the follow- Colman 3 causes the counters step to marked contacts binations I bein closed and a Hank being open: This contact connects alternating current from a l 15 volt AC "8 com g source through control power transformer CPT and half-wave 5 5 diode rectifiers D1 1 and D12 to units counter stepping magnet 100 200 300 400 500 600 700 800 900 0 UM and tens counter stepping magnet TM, respectively. Setting 10 20 30 40 50 0 These rectifiers pass spaced half-wave pulses of current to the switch contacts: 1 2 3 6 7 8 9 0 respective counter stepping magnets to pulse them. This 4 x causes units counter UC to be stepped clockwise to contact 7 i I: 60 and tens counter TC to be stepped clockwise to contact 8. At x contact 7. units counter UC connects positive voltage from contact 6 of switch US through diode rectifier D13 to units stepping magnet UM to maintain it energized. This. stops units: In the 16 operating positions of the fractions switch unit, the Counter Uc 011 Contact T In 5 l17lnfi1afifleh at 6053867871 four contacts close in the following binary combinations: 65 tens counter TC connects positive voltage from contact 7 of Settinc...... l '2 3 i i 6 7 8 9101112 1314 15 0 Switch contacts:

4 x x x x x x x x .x x x x x x x 2... x x x x l. x x x x. 1 x. x x x x. x x ..x

In this manner. the hundreds switch unit H will pass outswitch TS through diode rectifier D14 to tens stepping magnet put pulses for lOO input pulses when its single connected con- 75 TM to maintain it energized. This stops the tens digit counter on contact 8 Sheet counters UC and TC are of the count down type, meaning that they operate in response to input pulses to step from the preset count down to zero, that is, clockwise in the drawing. The movable contact steps on deenergization of the associated stepping magnet. Consequently, it is necessary to connect these counters to the count select switches in the manner shown, that is, each contact of the switch is connected to the next higher numbered contact of the associated counter, to compensate for the single stepping of each counter which unavoidably occurs when relay CTR is deenergized as hereinafter described.

Also, as a result of operation of the preset switch to close its contact 2 in FIG. 10, the knife speed is preset to cut the correct length of sheet as near as possible under the control of preset reference tachometer PT3.

This contact 2 of the preset switch energizes top knife preset relay PRE across the DC supply lines. This relay closes its contacts I and 2 and opens its contact 3 in FIG. la. This relay also closes its contacts 4, and 6 in FIG. 1c.

Contact 4 completes a self-maintaining circuit for the operating coil of the preset relay so that the preset pushbutton switch may be released to allow it to reopen. This self-maintaining circuit extends through normally closed contact 3 of relay LS in shunt of contact 2 of the preset switch.

Reopening of contact 1 of the preset switch deenergizes count transfer relay CTR to reopen its contacts 1 and 3 and to reclose its contact 2. Contact I deenergizes units and tens counter stepping magnets UM and TM. Since these counters are the type that step on deenergization as aforesaid, this will cause units counter UC to step to contact 6 and will cause tens counter to step to contact 7. These counters have nowbeen set to 67 sheets as selected on the count select switches.

Contact 1 of preset relay PRE connects feedback pulse tachometer PT4 to NOT logic N2. Contact 2 of this preset relay connects preset reference tachometer PT3 to NOT logic N l. Contact 3 opens a point in the circuit of pulse tachometer PTl. Contact 5 energizes reset relay RES across the DC source. And contact 6 energizes stepper relay STR across the l volt AC source. This relay closes and reopens its contact 1 on successive energizations of its operating coil.

RElay STR closes its contact 1 to energize top knife transfer relay 'I'IR. This transfer relay closes contact 1 and opens contact 2 to render scaler SCI effective and scaler SC2 ineffective in FIG. 10. Alternatively, run-transfer manual pushbutton switch RT may be pressed to energize relay STR or to deenergize it to transfer to a different selected length of cutoff piece.

Reset relay RES closes its contact 1 to connect output P of the pulse canceller to input R of the position pulse generator. This relay also opens its contact 2 to disconnect input K of the position pulse generator from output P of the pulse canceller. This conditions the position pulse generator for shifting the bit from output 3 in response to input pulses.

As a result, preset reference pulses and feedback pulses are applied to the frequency based regulator in FIG. la. These pulses cause the frequency based regulator to operate as.

hereinbefore described. Assuming that the knife speed is too slow for the 154% inch length cut selected on sheet length control switches SLCI, the frequency of the pulses coming out of power AND logic A1 in FIG. 1b will be higher than the frequency of the pulses coming out of power AND logic A2. Since the width of both of these pulses is equal and constant and their frequency differs, an integrator is provided to sense this difference and to initiate the proper control function.

This integrator is shown in FIG. lb as a magnetic amplifier means. This means comprises a top knife faster magnetic amplifier TFX and a top knife slower magnetic amplifier TSX. Faster magnetic amplifier TFX controls the firing angle of forward semicondu ctor controlled rectifiers SCRl and SCR3 to run the correction motor in the forward direction. This adjusts the mechanical variable speed drive in a manner to increase the knife speed. Slower magnetic amplifier TSX controls the firing angle of reverse semiconductor controlled rectifiers SCR2 and SCR4 to run the correction motor in the LII reverse direction. This adjusts the mechanical variable speed MTl and MT2, a center-tapped armature resistor AR, and the aforementioned pairs of forward rectifiers SCRl and SCR3 and reverse rectifiers SCR2 and SCR4.

From the foregoing; it will be apparent that when forward rectifiers SCRl and SCR3 are fired into conduction, transformer MTl will cause current to flow through SCRI, the left half of resistor AR and down through the armature on one half-cycle of the source voltage. On the other half-cycle, transformer MT2 will cause current to flow through rectifier SCR3, the right half of resistor AR and down through the armature. Thus, the armature is provided with full-wave rectified forward voltage whose magnitude is controlled by the firing angle of rectifiers SCRl and SCR3.

On the other hand, when reverse rectifiers SCR2 and SCR4 are fired into conduction, transformer MTl will cause current to flow up through the armature, the left half of resistor AR and rectifier SCR2 on one half-cycle of the source voltage. On the other half-cycle, transformer MT2 will cause current to flow up through the armature, the right half of resistor AR and rectifier SCR4. Thus, the armature is provided with full-wave rectified reverse voltage whose magnitude is controlled by the firing angle of rectifiers SCR2 and SCR4.

Faster magnetic amplifier TFX has two power windings PW] and PW3 for controlling the firing angle of rectifiers SCRI and SCR3, respectively. These power windings are supplied with voltage from respective secondary windings of a transformer TRl whose primary winding is supplied with AC voltage in parallel with a portion of the primary winding of motor transformer MTl. Power winding PWl is connected in series with one secondary winding of transformer TRI and a unidirectional diode D15 across the gate and cathode of rectifier SCRl, there being a resistor R35 connected across this gate-cathode junction to provide the proper firing current to the gate. Power winding PW3 is similarly connected in series with the other secondary winding of the transformer and a diode D16 across the gate and cathode of rectifier SCR3, there being a resistor R36 across the gate-cathode junction.

Slower magnetic amplifier TSX is similarly supplied from a transformer TR2 in parallel with transformer TRl and has similar power windings PW2 and PW4, diodes D17 and D18 and resistors R37 and R38 similarly connected to control firing of rectifiers SCR2 and SCR4.

The power windings of faster magnetic amplifier TFX are magnetically coupled to four control windings including a bias winding BF, a speed control winding SF, a position control winding PF, and a jog control winding J F.

In a similar manner, the power windings of slower magnetic amplifier TSX are magnetically coupled to four control windings including a bias winding BS, a speed control winding SS, a position control winding PS, and a jog control winding J S.

Bias windings BF and BS are energized from DC source P-N. For this purpose, the resistors of a pair of potentiometers POTl and POT2 are connected in parallel across the DC source. Bias winding BF is connected from the movable tap of potentiometer POTI to negative side N of the DC supply. Likewise, bias winding BS is connected from the movable tap 9i aet t sn ta oll 91h? F fl sj i 'i Qt t QDQsL Et Turning these potentiometers clockwise will increase the e i ergiza tion of the bias windings.

The control windings of the magnetic amplifiers have been illustrated such that current flow in the left direction turns the amplifier toward off and current flow in the right direction through the winding turns the amplifier toward on.

With this in mind, the potentiometers are preferably adjusted to cause the bias windings to turn the amplifiers a certain amount beyond cutoff. This provides a deadband of the desired width to prevent the amplifier from being too sensitive to error signals. g 7 V For speed regulation purposes, the output of power AND logic Al is connected through speed control winding SF of the faster magnetic amplifier in the right-hand, tum-on direction and then through speed control winding SS of the slower magnetic amplifier in the left-hand, turnoff direction, variable resistor VR! and normally open contact SR1 in parallel, a resistor R39 and a variable resistor VR2 to the negative side of the 24 volt DC source. The output of power AND logic A2 is connected through variable resistor VR! and open contact SR1 in parallel and then through speed slower control winding SS in the right-hand, turn-on direction and speed faster control winding SF in the left-hand, turnoff direction and a resistor R40 to the negative side of the 24 volt DC source.

With this arrangement, when the output signal from power AND logic Al is greater than the output signal from power AND logic A2, faster magnetic amplifier TFX will be turned on. On the other hand, when the output signal from power AND logic A2 is larger, slower magnetic amplifier TSX will be turned on. Variable resistor VR2 is used to adjust the balance between the speed reference and speed feedback outputs so that proper correction motor operation is attained. Turning it clockwise increases the effectiveness of the speed faster controlv Variable resistor VRI is used to adjust the speed gain for both signals. Turning this variable resistor clockwise increases the gain. Contact SR1 may be closed to provide maximum gain up to a web speed For position regulation purposes, output P of output pulse generator OPG is connected in the right-hand direction through position control winding PF of the faster magnetic amplifier and then through an on-off switch contact NF that is closed when the system is turned on to the negative side of a volt DC source. Output T of the output pulse generator is connected in the right-hand direction through position control winding PS of the slower magnetic amplifier and then through contact NF to the negative side of the 10 volt DC source. As will be apparent, whenever there is a position signal at output P, position faster winding PF will be energized to turn the faster amplifier a small amount on. And whenever there is a position signal at output T, position slower winding PS will be energized to turn the slower amplifier a small amount on.

Control windings JF and 3S allow manual jogging control of the correction motor. For this purpose, the positive side P of the 24 volt DC source is connected through a jog shorter pushbutton switch SH, a resistor R41, jog faster control winding JF in the right-hand turn-on direction, winding .15 in the left-hand turnoff direction, and resistor R42 to the negative side of the 24 volt DC source. Depressing jog shorter pushbutton SH will cause adjustment of the mechanical variable speed drive whereby the knife will cut a shorter sheet, hence the name jog shorter. The positive side of the 24 volt DC source, is also connected through a resistor R43, jog slower control winding JS in the right-hand turn-on direction, winding J F in the left-hand turnoff direction, resistor R44 and a jog longer pushbutton switch L0 to the negative side of the DC source. Depressing jog longer pushbutton L0 will cause the knife to cut a longer sheet.

If thereference and feedback pulses are out of phase, a

signal will appear at either output P or T of the output pulse generator to energize either winding PF or PS sufficiently to rotate the correction motor to compensate for the out of phase condition between the corrugated board and the cutoff E lis-Mn. an,

and the number of sheets desired (67) having been registered in the predetermining counter, the system is ready to start running corrugated board. This is done by engaging clutch CL between the main motor and the double-facer. This causes the double-facer to start moving the corrugated board.

As soon as the corrugated board starts moving, preset pulse tachometer PT3 is switched out and cutting reference pulse tachometer PT] driven by the web rider is switched in. For this purpose, the web rider wheel upon detection of initial board movement, operates pulse tachometer PT2 to generate a pulse, one pulse per 1/100 inch of board movement. This is a negative voltage pulse and is applied through a resistor R45 and rectifier bridge R82 to the lower input terminal lN of transistor circuit 24. This causes a pulse of current to flow from positive side P of a DC source through a resistor R46 and rectified bridge R82 to the upper input terminal IN of a transistor circuit 24. A capacitor C10 is connected across resistor R46 to absorb transient voltages and prevent inadequate operation of the transistor circuit. A unidirectional diode D19 is connected from the lower input terminal of rectifier bridge R82 to the upper input terminal thereof to shunt any reverse voltage from this circuit. A capacitor C11 is connected across the input terminals of transistor circuit 24 to smooth the voltage at these input terminals to cause relay LS to operate. w

Relay LS upon energization as aforesaid closes its contacts 1, 2, 4 and 5 and opens its contact 3. This contact 3 interrupts the maintaining circuit of preset relay PRE to deenergize this relay. Contact l maintains feedback tachometer PT4 connected to NOT logic N2. Contact 2 closes a point in the circuit of cutting reference tachometer PT]. And contact 4 of relay LS closes a maintaining circuit for relay RES. Relay LS remains energized as long as tachometer PT2 generates pul- Relay PRE upon deenergizing open contact 1 without effect, opens contact 2 to disconnect preset reference tachometer PT3 from NOT logic N1, closes contact 3 to connect cutting reference tachometer PTl to NOT logic N1 through contact 2 of relay LS that just closed, opens at contact 4 is self-maintaining circuit, opens contact 5 without effect as reset relay RES is maintained through contact 4 of relay LS that just closed, and opens at contact 6 the energizing circuit of stepper relay STR. However, relay STR maintains its conssstlsl ssi so The frequency based regulator now receives cutting reference pulses from tachometer PTl in accordance with the actual measurement of the moving board. It also receives feedback pulses from tachometer PT 4. As a result, the frequency based regulator controls the correction motor in accordance with the speed error and position error signals to cut sheets to accurate length.

it will be recalled that when relay LS was energized at initiation of movement of the corrugated board, it closed its contact 5 at the lower right-hand portion of FIG. 1a. This causes positive voltage to be applied to the first input of power AND logic A3. Positive voltage is also applied to the second input of this power AND logic through normally closed contact 3 of the zero relay. These two contacts are interlocks that must be in their proper positions before sheet count pulses can pass through AND logic A3 in FIG. lb.

Counting of cut sheets will now be described. it will be re called the! L600 pulses are generated by tachometer PM for each revolution of the knife. These pulses are counted by counters BCDl, BCD2 and BC] in FIG. la. As shown in the above table, for 1,600 pulses coming into these counters out- The top knife now having been preset to the cutoff speed put terminal C of counter unit BCl provides one positive pulse from the I bit side of the fourth flip-flop therein. Output B of this counter unit BC I is connected to the bit side of this fourth flip-flop so that one pulse of opposite polarity appears thereat for each set of 1.600 pulses coming from the knife tach. If it is assumed that all three of these counter units are at zero to stan out, output B of counter unit BCI will be at positive voltage and will go negative at the eighth pulse into this unit (eight hundredth pulse from tach. PT4) when output C goes positive. Output B will then go back to positive when the unit resets on the sixteenth pulse thereto (sixteen hundredth pulse from tach. PT4). This positive voltage from output B is applied to the third input ofpower AND logic A3.

From the foregoing, it will be apparent that power AND logic A3 will have positive voltage on all three inputs upon the closure of contact 5 of relay LS. As a result, the positive voltage output of this power AND logic is applied through contact I of add-on control relay A0 in FIG. 1c and diode D to the operating coil of units magnet UM to energize this magnet. 20

The sheet counters will continue counting in that manner until the preselected number of 67 sheets has been cut. At such time both counters will reach zero and close contacts UM] and TMl to energize the zero relay. This relay will open its contacts I and 3 and close its contact 2. Contact 3 in FIG. la disconnects positive voltage from the second input of power AND logic A3 to cause the latter to stop passing pulses to the sheet counters. Contacts 1 and 2 pulse the stop relay to stop the main motor. As will be apparent, before the zero relay energized. current flowed through contact 1 thereof and' through resistor R47 to charge capacitor C12. Now when contact 1 opens and contact 2 closes, capacitor C12 discharges through contact 2, the operating coil of the stop relay and resistor R47 to energize the stop relay for an interval of time. As indicated by its contacts, the stop relay may be used to stop the double-facer by stopping the main motor or may be used to initiate operation of an automatic order changer whereby the machine starts cutting sheets for another order preselected on switches SLC2.

An add-on counter is shown at the upper right-hand portion of FIG. 1c. This counter permits adding on to the count previously set on count select switches US and TS. This adding on 5 can be done while the cutofi machine is running. For example, if defective sheets have been cut and it is desired to add 15 sheets to the order of 67 sheets, this can be done by the add-on counter.

Following registration of this count on the add-on counter, add-on start pushbutton switch SP8 is pressed. This causes energization of add on control relay A0 through contact 1 of add-on units magnet AUM and contact I of add-on tens magnet ATM in parallel across the 24 volt DC supply. It will be apparent that these contacts are open at the zero position of the add-on counters and are closed in all other positions thereof.

Add-on control relay A0 opens its contact I to disconnect 70 the sheet counter from the pulse input and closes its contacts 2 and 3 to connect such pulse input to add-on units magnet AUM. Relay A0 also closes its contact 4 to complete a selfmaintaining circuit in shunt of the add-on start switch so that it may be released to allow it to reopen.

Sheet count pulses now come into the add-on counter until it counts out at 15 and automatically shifts the pulse input back to the sheet counter. At the fifth pulse, the add-on units counter reaches zero and closes its contact 2 and opens its contact I. The opening of contact 1 is without efiect at this time since contact 1 of the add-on tens magnet is closed in parallel therewith. However, contact 2 of add-on units magnet AUM connects the pulse input to add-on tens magnet ATM also. The sixth pulse then steps the add-on tens counter to zero and steps the add-on units counter to nine. This causes contacts I of the add-on units magnet to reclose to maintain relay A0 energized while contact 1 of the add-on tens magnet opens at its zero position. Contact 2 of the add-on units magnet reopens so that no further pulses go to the add-on tens counter. The ensuing pulses then step the add-on counter until at the fifteenth pulse it reaches zero again and opens its contact 1. This causes relay A0 to be deenergized. As a result, relay A0 opens its contacts 2 and 3 to disconnect the pulse input from the add-on counter and recloses its contact 1 to reconnect the pulse input to the sheet counter. At contact 4 relay A0 interrupts its self maintaining circuit. The sheet counter then resumes counting with 15 sheets having been added to the order.

Sheet length readout 20 at the upper portion of FIG. lb displays the actual length of every second sheet to an accuracy of one one-hundredth of an inch as measured by the web rider. For this purpose, the web rider wheel in FIG la operates tachometer PT2 to provide one pulse per one-hundredth inch of board. These pulses are applied to input terminal IN of the 0 sheet length readout device in FIG. 1b. This sheet length readout device is supplied at supply terminals S1 and S2 with I 15 volts from an AC source. This sheet length readout device is turned on along with being reset to zero and turned off in response to alternate closings of its reset reed switch RRS. Cyclic mechanism 16 momentarily closes this reset reed switch once for each revolution of the knife. The first closing of this reset reed switch will enable it to receive pulses from tachometer PT2 to display the length of the sheet. The second closing will turn it off so that it will not measure the second sheet. The third closing will reset it to zero and condition it to receive pulses thereby to display the length of the third sheet, etc. Tenninal DC of the sheet length readout device is supplied with positive voltage from supply conductor P to enable it to respond to the negative going pulses coming into its input 5 terminal IN.

Footage counter 22 indicates in ten foot increments the amount of corrugated board that has been used. It is provided with an amplifier supplied from a DC source and having its input terminals connected across reed switch RS. This reed switch is operated by the web rider to provide one pulse per ten feet of board. A footage counter operating magnet 22a is connected between the amplifier output terminal and the negative side of the DC source. This operating magnet operates indicator number wheels 22b or the like to display the pulse count. This count when multiplied by ten indicates the footage of board that has been used.

The component circuits and devices that have been shown schematically in the drawings as by rectangles or the like are conventional features whose detailed illustration is not essential for a proper understanding of the invention. Exemplary circuits and devices usable therefor are identified as follows:

NOT logic Nl-Cutler-Hammer NOT Inverter Board No. 3.

Binary Counter BCl and Binary Coded Decimal Counter BCDl-Cutler-Hammer Four Bit Binary Counter Board No. 16.

Thumb Wheel Switch SLClChicago Dynamic Industries Thumb Wheel Switch.

Scaler SCI-Cutler-Hammer Scaler Board No. 22.

Pulse Canceller PC-Cutler-I-Iammer Pulse Canceller Board No. 24.

Position Pulse Generator PPG-Cutler-I-Iammer Position Pulse Generator Board No. 26.

Output Pulse Generator OPGCutler-Hammer Pulse Output Module (Magnetic Comparison) Board No. 25.

Sheet Length Readout Device -Gated Totalizer by Dynapar, a division of Louis Allis Co.

Footage Counter 22-Electromechanical Counter Model 7-Y-l-RNF-PN, Durant Manufacturing Co.

Transistor Circuit 24Cutler-Hammer Type TF Standard Duty Transistor Sensitive Relay,

Catalog No. 13535.

Count Select Switches US and TS-Durant Manufacturing Co. 40500 Series Uniset Switches.

Sheet Counters and Add-on Counters-Durant Manufacturing Co. 49000 Series Unipulser Counters.

While the apparatus hereinbefore described is effectively adapted to fulfill the objects stated, it is to be understood that the invention is not intended to be confined to the particular preferred embodiment of frequency based knife control systems disclosed, inasmuch as it is susceptible of various modifications without departing from the scope of the invention.

We claim:

1. In a knife control apparatus for providing accurate control of the length of pieces cut off from a high-speed, continuously moving elongated stock material, the apparatus having a main motor and means clutched thereto for moving the stock material past a cyclic cutoff knife, means comprising a variable speed drive mechanism powered by the main motor for driving the cutoff knife and being adjustable to control the speed of the cutoff knife relative to the stock material speed, and a .reversible correction motor for adjusting the variable speed drive mechanism, the improvement comprising:

a frequency-based control system for providing an error signal at any time during operation of the apparatus that a variation in a preselected operating condition of the knife relative to movement of the stock material is detected comprising:

reference pulse generating means for providing a train of pulses of a frequency proportional to the stock material speed;

feedback pulse generating means for providing a fixed number of pulses per cycle of the cutoff knife and having a frequency proportional to the speed thereof;

means for continuously comparing during a given cutoff knife cycle the reference and feedback pulse trains to detect a difference therein that occurs whenever the knife operation varies from proper synchronism with the advancement of the piece of stock material to be cut off;

means responsive to detection of such difference for providing an error signal during such given cycle;

and means responsive to said error signal for operating the correction motor during such given cycle to adjust the variable speed drive mechanism in an amount and direction to bring the knife cycle into said proper synchronism thereby to afford accurate control of the length of the pieces that are cut off.

2. The invention defined in claim 1 together with:

manually settable means for selecting a desired length for the pieces to be cut off;

and means responsive to said manually settable means when set for a given length for passing a number of feedback pulses proportional thereto and for deleting the remainder of the fixed number of pulses per cycle of knife operation.

3. The invention defined in claim 1, wherein said reference pulse generating means comprises:

a preset reference pulse generator driven by the main motor for generating one pulse per simulated unit length of stock material;

a cutting reference pulse generator driven by the moving material for generating one pulse per unit length of moving material;

means for connecting said preset reference pulse generator to the frequency based control system to preset the cutoff knife cycle as near as possible into said proper synchronism before any stock material is moved;

and means operable upon initiation of movement of stock material for disconnecting said preset reference pulse 5 generator and for connecting said cutting reference pulse generator to the frequency based control system.

4. The invention defined in claim 1, wherein said means for continuously comparing the reference and feedback pulse trains comprises:

speed control means for adjusting the speed of the cutoff knife as a function of the frequency difference between the reference and feedback pulses;

and position control means for adjusting the phase of the knife cycle with respect to a properly corresponding point on the moving piece to be cut for proper synchronism therebetween,

5. The invention defined in claim 1, together with:

manually settable means for selecting a desired number of pieces to be cut for a single order;

a counter for automatically counting the pieces as they are cut;

means operable to transfer the setting of said manually settable means to said counter;

means responsive to operation of said frequency based control system for causing said counter to count once for each cycle of the cutoff knife;

and means responsive to said counter counting out for stopping the apparatus from cutting any further pieces for that order.

6. The invention defined in claim 5, together with:

an add-on counter manually settable to add a desired number of pieces to the order previously registered in the first-mentioned counter;

and means for temporarily substituting said add-on counter in place of said first-mentioned counter for counting pieces until it counts out and then transferring back to said first-mentioned counter to resume counting of the balance of the order after the add-on pieces have been cut.

7. The invention defined in claim 1, together with:

a sheet length readout device for displaying the length of the sheets being cut;

means responsive to movement of the stock material for operating said sheet length readout device;

and means responsive to cyclic operation of said cutoff knife for cycling said sheet length readout device to display the length of alternate sheets.

8. The invention defined in claim 1, together with:

a footage counter for displaying the total length of stock material that has been used;

and means responsive to movement of said stock material for operating said footage counter.

9. The invention defined in claim 1, wherein said means for continuously comparing the reference and feedback pulse trains comprises:

means for shaping said pulses of both the reference and feedback pulse trains to uniform widths;

and said means responsive to detection of a difference in the reference and feedback pulse trains comprises integrator means responsive to the difference in the frequencies of the uniform width pulse trains for providing said error signal.

10. The invention defined in claim 9, wherein said means responsive to said error signal comprises:

means for operating the correction motor and the variable speed drive mechanism to adjust the speed of the cutoff knife for accurate cutoff of the correct length of piece.

11. The invention defined in claim 1, wherein said means 70 for continuously comparing the reference and feedback pulse trains comprises:

means for cancelling coincident pulses in the two trains.

that is, pulses whose leading edges are within a predetermined time limit of each other, and for passing the pulses outside such time limit for position control;

a position pulse generator responsive to the trains of out of phase pulses passed by said cancelling means for providing a first pulse train output when the reference pulses lead the feedback pulses or to provide a second pulse train when the feedback pulses lead the reference pulses, said first and second pulse trains having a pulse width proportional to their phase displacement and a frequency proportional to the stock material speed;

and said means responsive to detection of a difference in the reference and feedback pulse trains comprises integrator means responsive to said first or said second pulse train for providing said error signal.

12. The invention defined in claim 11, wherein said means responsive to said error signal comprises:

means for rotating the correction motor to adjust the variable drive mechanism and to adjust the position of the cutoff knife relative to the position of the moving stock material for accurate cutoff of the correct length of piece.

13. In a knife control apparatus for providing accurate control of the length of sheets cut off from a high-speed, continuously moving web, the apparatus having web forming and moving means, a main motor and a clutch operable to couple the main motor to the web moving means to move the web past a cyclic cutoff knife, the combination comprising:

a variable speed drive mechanism driven by the main motor for driving the cyclic cutoff knife;

a correction motor coupled to said variable speed mechanism;

motor control means responsive to an error signal for operating said correction motor in the proper direction to adjust the variable speed drive mechanism thereby to adjust the cutoff knife cycle relative to the web speed and control the cutofflength ofthe sheets;

and a frequency based control system for continuously monitoring the cutoff length of the sheets and for providing an error signal whenever a variation from a preselected sheet length is detected comprising:

reference pulse generating means for providing a train of pulses having a frequency proportional to the stock material speed;

feedback pulse generating means for providing a fixed number of pulses per operating cycle of the cutoff knife having a frequency proportional to the cutoff knife speed;

cutoff length selecting means settable for a desired length of sheets to be cut thereby selecting a portion of said fixed number of feedback pulses and deleting the remainder thereof per cycle of the cutoff knife;

means for comparing the reference pulses and selected portion of feedback pulses to detect a difference thereon indicative of a deviation between web movement and knife operation that will produce an incorrect length if left uncorrected;

and means responsive to detection of such difference for providing a directional error signal for operating said motor control means to correct such deviation.

14. The invention defined in claim 13, wherein said means responsive to detection of such difference for providing a directional error signal comprises:

dead band providing means whereby said directional error signal providing means provides an error signal only when said difference is above a predetermined adjustable value thereby to stabilize the corrective action.

15. The invention defined in claim 13, wherein said cutoff length selecting means comprises:

a counter for counting said feedback pulses having a plurality of outputs providing pulse trains of a plurality of frequencies indicative of a plurality of progressive percentages, respectively, of the total length of sheet for a given web speed;

manual switches connected to said outputs operable to select the sheet length in terms of small fractions of an inch by closing the proper contacts thereby deleting the pulses coming to the contracts left open;

and a scaler connected to said switches for receiving a plurality of different frequency pulse trains of noncoincident pulses and providing a single train of pulses equal to the sum thereof for comparison with said reference pulses.

16. The invention defined in claim 15, wherein said cutoff length selecting means also comprises:

a second set of like manual switches connected in series to the outputs of said counter in parallel with the first-mentioned switches;

and means for switching either the first or the second set of switches into operative connection in the system to control the length of sheet whereby when one set of such switches is in use, the other set of switches can be preset and switched in at the appropriate time to change the length of sheets that are cut.

17. The invention defined in claim 15, wherein said means for comparing the reference pulses and selected portion of feedback pulses comprises:

means for making a first comparison of said reference pulses and selected portion of feedback pulses to detect a difierence in their frequencies;

and means for making a second comparison of said reference pulses and selected portion of feedback pulses to detect a difference in their phases for knife position regulation;

and said means for providing a directional error signal comprises:

means responsive to the difference in their frequencies for providing a knife speed error signal having a polarity according to which frequency is higher and a magnitude proportional to the frequency difference;

and means responsive to the difference in phases for providing a knife position error signal having a polarity according to which pulses are leading and a magnitude proportional to the phase difference.

18. The invention defined in claim 17, wherein said means for making a second comparison comprises:

a pair of frequency dividers for the reference pulses and selected portion of feedback pulses, respectively, affording selection of the gain for best performance of the knife position regulation;

and a pulse canceller connected to said frequency dividers for cancelling pulses whose leading edges coincide within a predetermined time limit and for passing both reference pulses and feedback pulses whose leading edges are displaced more than said limit;

and a reversible shift register connected to said pulse canceller for providing one or another pulse output according to which pulses have a leading phase and having a pulse width proportional to the phase difference.

19. In a frequency based knife control system for providing accurate control of the length of pieces cut off from a highspeed continuously moving elongated stock material, the system having a main motor and means powered thereby for driving the stock material past a rotary cutoff knife, and means comprising a variable speed drive mechanism powered by the main motor for driving the cutoff knife and being adjustable to control the speed thereof, the improvement comprising:

reference pulse generating means for generating pulses of a frequency proportional to the speed of the stock material;

feedback pulse generating means for generating a fixed number of pulses per cycle of the cutoff knife;

cutoff length selecting means settable for a desired length of pieces to be cut thereby selecting a portion of said fixed number of feedback pulses and deleting the remainder thereof;

a reversible correction motor coupled to the variable speed drive mechanism for adjusting it to increase or decrease the speed of the cutoff knife relative to the speed of the main motor;

control means for said correction motor operable to run it in the forward or reverse direction;

pulse integrator means for controlling said motor control means comprising speed control means responsive to said reference pulses or the selected portion of said feedback pulses having the higher frequency for controlling said motor control means in a manner to run the correction motor in the proper direction to adjust the speed of the cutoff knife and to reduce the frequency difference of the reference and feedback pulses;

pulse canceller means for cancelling reference and feedback pulses that have a phase coincidence within a predetermined time limit and for passing reference and feedback pulses that have a larger phase difference;

means responsive to the pulses passed by said pulse canceller means for producing position faster or position slower control pulses according to whether the reference or the feedback pulses have a leading phase, these pulses having a width proportional to such phase difference and a frequency proportional to the speed of the stock material;

and said pulse integrator means also comprising position control means responsive to said position or said position slower control pulses for controlling said motor control means in a manner to rotate the correction motor in the proper direction to adjust the rotary position of the cutoff knife into correct phase with a given point on the piece of advancing stock material to be cut and to reduce the noncoincidence of the phases of the reference and feedback pulses. 

1. In a knife control apparatus for providing accurate control of the length of pieces cut off from a high-speed, continuously moving elongated stock material, the apparatus having a main motor and means clutched thereto for moving the stock material past a cyclic cutoff knife, means comprising a variable speed drive mechanism powered by the main motor for driving the cutoff knife and being adjustable to control the speed of the cutoff knife relative to the stock material speed, and a reversible correction motor for adjusting the variable speed drive mechanism, the improvement comprising: a frequency-based control system for providing an error signal at any time during operation of the apparatus that a variation in a preselected operating condition of the knife relative to movement of the stock material is detected comprising: reference pulse generating means for providing a train of pulses of a frequency proportional to the stock material speed; feedback pulse generating means for providing a fixed number of pulses per cycle of the cutoff knife and having a frequency proportional to the speed thereof; means for continuously comparing during a given cutoff knife cycle the reference and feedback pulse trains to detect a difference therein that occurs whenever the knife operation varies from proper synchronism with the advancement of the piece of stock material to be cut off; means responsive to detection of such difference for providing an error signal during such given cycle; and means responsive to said error signal for operating the correction motor during such given cycle to adjust the variable speed drive mechanism in an amount and direction to bring the knife cycle Into said proper synchronism thereby to afford accurate control of the length of the pieces that are cut off.
 2. The invention defined in claim 1 together with: manually settable means for selecting a desired length for the pieces to be cut off; and means responsive to said manually settable means when set for a given length for passing a number of feedback pulses proportional thereto and for deleting the remainder of the fixed number of pulses per cycle of knife operation.
 3. The invention defined in claim 1, wherein said reference pulse generating means comprises: a preset reference pulse generator driven by the main motor for generating one pulse per simulated unit length of stock material; a cutting reference pulse generator driven by the moving material for generating one pulse per unit length of moving material; means for connecting said preset reference pulse generator to the frequency based control system to preset the cutoff knife cycle as near as possible into said proper synchronism before any stock material is moved; and means operable upon initiation of movement of stock material for disconnecting said preset reference pulse generator and for connecting said cutting reference pulse generator to the frequency based control system.
 4. The invention defined in claim 1, wherein said means for continuously comparing the reference and feedback pulse trains comprises: speed control means for adjusting the speed of the cutoff knife as a function of the frequency difference between the reference and feedback pulses; and position control means for adjusting the phase of the knife cycle with respect to a properly corresponding point on the moving piece to be cut for proper synchronism therebetween.
 5. The invention defined in claim 1, together with: manually settable means for selecting a desired number of pieces to be cut for a single order; a counter for automatically counting the pieces as they are cut; means operable to transfer the setting of said manually settable means to said counter; means responsive to operation of said frequency based control system for causing said counter to count once for each cycle of the cutoff knife; and means responsive to said counter counting out for stopping the apparatus from cutting any further pieces for that order.
 6. The invention defined in claim 5, together with: an add-on counter manually settable to add a desired number of pieces to the order previously registered in the first-mentioned counter; and means for temporarily substituting said add-on counter in place of said first-mentioned counter for counting pieces until it counts out and then transferring back to said first-mentioned counter to resume counting of the balance of the order after the add-on pieces have been cut.
 7. The invention defined in claim 1, together with: a sheet length readout device for displaying the length of the sheets being cut; means responsive to movement of the stock material for operating said sheet length readout device; and means responsive to cyclic operation of said cutoff knife for cycling said sheet length readout device to display the length of alternate sheets.
 8. The invention defined in claim 1, together with: a footage counter for displaying the total length of stock material that has been used; and means responsive to movement of said stock material for operating said footage counter.
 9. The invention defined in claim 1, wherein said means for continuously comparing the reference and feedback pulse trains comprises: means for shaping said pulses of both the reference and feedback pulse trains to uniform widths; and said means responsive to detection of a difference in the reference and feedback pulse trains comprises integrator means responsive to the difference in the frequencies of the uniform width pulse trains for providing said error signal.
 10. The invention defined in claim 9, wherein said meaNs responsive to said error signal comprises: means for operating the correction motor and the variable speed drive mechanism to adjust the speed of the cutoff knife for accurate cutoff of the correct length of piece.
 11. The invention defined in claim 1, wherein said means for continuously comparing the reference and feedback pulse trains comprises: means for cancelling coincident pulses in the two trains, that is, pulses whose leading edges are within a predetermined time limit of each other, and for passing the pulses outside such time limit for position control; a position pulse generator responsive to the trains of out of phase pulses passed by said cancelling means for providing a first pulse train output when the reference pulses lead the feedback pulses or to provide a second pulse train when the feedback pulses lead the reference pulses, said first and second pulse trains having a pulse width proportional to their phase displacement and a frequency proportional to the stock material speed; and said means responsive to detection of a difference in the reference and feedback pulse trains comprises integrator means responsive to said first or said second pulse train for providing said error signal.
 12. The invention defined in claim 11, wherein said means responsive to said error signal comprises: means for rotating the correction motor to adjust the variable drive mechanism and to adjust the position of the cutoff knife relative to the position of the moving stock material for accurate cutoff of the correct length of piece.
 13. In a knife control apparatus for providing accurate control of the length of sheets cut off from a high-speed, continuously moving web, the apparatus having web forming and moving means, a main motor and a clutch operable to couple the main motor to the web moving means to move the web past a cyclic cutoff knife, the combination comprising: a variable speed drive mechanism driven by the main motor for driving the cyclic cutoff knife; a correction motor coupled to said variable speed mechanism; motor control means responsive to an error signal for operating said correction motor in the proper direction to adjust the variable speed drive mechanism thereby to adjust the cutoff knife cycle relative to the web speed and control the cutoff length of the sheets; and a frequency based control system for continuously monitoring the cutoff length of the sheets and for providing an error signal whenever a variation from a preselected sheet length is detected comprising: reference pulse generating means for providing a train of pulses having a frequency proportional to the stock material speed; feedback pulse generating means for providing a fixed number of pulses per operating cycle of the cutoff knife having a frequency proportional to the cutoff knife speed; cutoff length selecting means settable for a desired length of sheets to be cut thereby selecting a portion of said fixed number of feedback pulses and deleting the remainder thereof per cycle of the cutoff knife; means for comparing the reference pulses and selected portion of feedback pulses to detect a difference thereon indicative of a deviation between web movement and knife operation that will produce an incorrect length if left uncorrected; and means responsive to detection of such difference for providing a directional error signal for operating said motor control means to correct such deviation.
 14. The invention defined in claim 13, wherein said means responsive to detection of such difference for providing a directional error signal comprises: dead band providing means whereby said directional error signal providing means provides an error signal only when said difference is above a predetermined adjustable value thereby to stabilize the corrective action.
 15. The invention defined in claim 13, wherein said cutoff length selecting means comprises: a counter for counting said feedback pulses haviNg a plurality of outputs providing pulse trains of a plurality of frequencies indicative of a plurality of progressive percentages, respectively, of the total length of sheet for a given web speed; manual switches connected to said outputs operable to select the sheet length in terms of small fractions of an inch by closing the proper contacts thereby deleting the pulses coming to the contracts left open; and a scaler connected to said switches for receiving a plurality of different frequency pulse trains of noncoincident pulses and providing a single train of pulses equal to the sum thereof for comparison with said reference pulses.
 16. The invention defined in claim 15, wherein said cutoff length selecting means also comprises: a second set of like manual switches connected in series to the outputs of said counter in parallel with the first-mentioned switches; and means for switching either the first or the second set of switches into operative connection in the system to control the length of sheet whereby when one set of such switches is in use, the other set of switches can be preset and switched in at the appropriate time to change the length of sheets that are cut.
 17. The invention defined in claim 15, wherein said means for comparing the reference pulses and selected portion of feedback pulses comprises: means for making a first comparison of said reference pulses and selected portion of feedback pulses to detect a difference in their frequencies; and means for making a second comparison of said reference pulses and selected portion of feedback pulses to detect a difference in their phases for knife position regulation; and said means for providing a directional error signal comprises: means responsive to the difference in their frequencies for providing a knife speed error signal having a polarity according to which frequency is higher and a magnitude proportional to the frequency difference; and means responsive to the difference in phases for providing a knife position error signal having a polarity according to which pulses are leading and a magnitude proportional to the phase difference.
 18. The invention defined in claim 17, wherein said means for making a second comparison comprises: a pair of frequency dividers for the reference pulses and selected portion of feedback pulses, respectively, affording selection of the gain for best performance of the knife position regulation; and a pulse canceller connected to said frequency dividers for cancelling pulses whose leading edges coincide within a predetermined time limit and for passing both reference pulses and feedback pulses whose leading edges are displaced more than said limit; and a reversible shift register connected to said pulse canceller for providing one or another pulse output according to which pulses have a leading phase and having a pulse width proportional to the phase difference.
 19. In a frequency based knife control system for providing accurate control of the length of pieces cut off from a high-speed continuously moving elongated stock material, the system having a main motor and means powered thereby for driving the stock material past a rotary cutoff knife, and means comprising a variable speed drive mechanism powered by the main motor for driving the cutoff knife and being adjustable to control the speed thereof, the improvement comprising: reference pulse generating means for generating pulses of a frequency proportional to the speed of the stock material; feedback pulse generating means for generating a fixed number of pulses per cycle of the cutoff knife; cutoff length selecting means settable for a desired length of pieces to be cut thereby selecting a portion of said fixed number of feedback pulses and deleting the remainder thereof; a reversible correction motor coupled to the variable speed drive mechanism for adjusting it to increase or decrease the speed of the cutoff knife relative to the speed Of the main motor; control means for said correction motor operable to run it in the forward or reverse direction; pulse integrator means for controlling said motor control means comprising speed control means responsive to said reference pulses or the selected portion of said feedback pulses having the higher frequency for controlling said motor control means in a manner to run the correction motor in the proper direction to adjust the speed of the cutoff knife and to reduce the frequency difference of the reference and feedback pulses; pulse canceller means for cancelling reference and feedback pulses that have a phase coincidence within a predetermined time limit and for passing reference and feedback pulses that have a larger phase difference; means responsive to the pulses passed by said pulse canceller means for producing position faster or position slower control pulses according to whether the reference or the feedback pulses have a leading phase, these pulses having a width proportional to such phase difference and a frequency proportional to the speed of the stock material; and said pulse integrator means also comprising position control means responsive to said position or said position slower control pulses for controlling said motor control means in a manner to rotate the correction motor in the proper direction to adjust the rotary position of the cutoff knife into correct phase with a given point on the piece of advancing stock material to be cut and to reduce the noncoincidence of the phases of the reference and feedback pulses. 